1. Field of the Invention
The present invention relates to a tristimulus calorimeter which measures the tristimulus color content of light incident thereon. More particularly, the invention relates to a template-type colorimeter in which both diffraction means for diffracting incident light and templates for spatially filtering the diffracted light are mounted on a common light-transparent substrate.
2. Description of the Related Art
Tristimulus calorimeters are instruments whose outputs are directly proportional to the tristimulus values of one or another of the CIE standard colorimetric observers, such as the CIE 1931 XYZ tristimulus values or RGB tristimulus values. Such instruments are useful in measuring the color content of light and they are used in connection with color reproduction, color matching, color research, etc.
Wyszecki, et al., at pages 243-248 in "Color Science: Concepts and Methods", John Wiley & Sons (1982), describe two different types of tristimulus colorimeters: filter-type calorimeters and template-type calorimeters. In filter-type calorimeters, three tristimulus filters are provided to filter radiant light, the spectral transmittance of the filters matching the desired CIE color-matching function. Three filtered light components from respective ones of the filters are measured by photo cells to provide the desired CIE tristimulus values. Filter-type colorimeters are inexpensive but are usually less accurate because of the difficulty in obtaining filters having the proper spectral transmittance functions.
In template-type calorimeters, radiant light is diffracted by diffraction means such as a diffraction grating or a prism into its spectral components. Templates having spatial filters which match the desired CIE color-matching functions are arranged to block some of the spectral components and to transmit only selected spectral components in accordance with the CIE color-matching function. Detectors are provided behind each template to measure the transmitted spectral components, thereby to output the desired CIE tristimulus values. Template-type calorimeters are accurate but they are more expensive.